11.3
Temperatura corporea
La temperatura corporea, misurata in gradi, è determinata dall'equilibrio tra la produzione di calore e la sua dissipazione verso l'ambiente circostan…
La temperatura corporea è la differenza tra la quantità di calore prodotta dal corpo e la quantità persa nell'ambiente esterno.
La temperatura corporea media di un adulto varia tra 97 °F e 99 °F.
L'ipotalamo è la struttura cerebrale responsabile della termoregolazione, l'equilibrio tra il calore perso e il calore prodotto.
L'ipotalamo anteriore controlla la perdita di calore principalmente attraverso la pelle.
Quando la temperatura aumenta, l'ipotalamo anteriore stimola il sistema nervoso simpatico ad aprire lo shunt atrioventricolare, una minuscola connessione tra le arteriole e le venule che causa vasodilatazione, per consentire al calore di fuoriuscire dalla pelle.
I meccanismi di perdita di calore si verificano attraverso l'evaporazione, l'irraggiamento, la convezione e la conduzione.
Allo stesso modo, l'ipotalamo posteriore regola la produzione di calore, principalmente attraverso il metabolismo.
Quando la temperatura diminuisce, l'ipotalamo posteriore segnala al sistema nervoso simpatico di chiudere lo shunt atrioventricolare, causando vasocostrizione per prevenire la perdita di calore.
I meccanismi che consentono la produzione di calore includono gli ormoni tiroidei, la piloerezione, i brividi e l'esercizio fisico.
View the full transcript and gain access to JoVE Core videos
Q1: What is body temperature and how does the body maintain it?
Body temperature is the balance between heat produced by the body and heat lost to the external environment. The average adult body temperature ranges from 97°F to 99°F. The hypothalamus, a brain structure, maintains this balance through thermoregulation by detecting temperature changes and activating heat production or loss mechanisms to keep core temperature constant despite environmental conditions.
Q2: How does the hypothalamus control heat loss when body temperature rises?
When temperature rises, the anterior hypothalamus stimulates the sympathetic nervous system to open arteriovenous shunts—tiny connections between arterioles and venules beneath the skin. This causes vasodilation, allowing blood to flow to the skin surface where heat escapes through evaporation, radiation, convection, and conduction, effectively cooling the body.
Q3: What mechanisms does the body use to produce heat when temperature drops?
When the posterior hypothalamus detects temperature below the setpoint, it activates heat production through metabolism, thyroid hormones, piloerection (goosebumps), shivering, and exercise. These mechanisms generate heat to maintain core body temperature. Simultaneously, vasoconstriction narrows blood vessels, reducing blood flow to skin and extremities to minimize heat loss.
Q4: What is the difference between core body temperature and surface body temperature?
Core body temperature, measured in deep tissues beneath the skin, typically ranges from 97.0°F to 99.5°F and remains relatively constant. Surface body temperature varies depending on blood circulation to the skin and heat dissipation. Core temperature is measured at tympanic or rectal locations using infrared thermometers, while surface temperature is measured orally, axillary, or on skin using thermometers or thermal imaging.
Q5: How does blood circulation contribute to heat transfer in the body?
Heat is produced by metabolic activities in core tissues and transmitted to the skin's surface by circulating blood. At the skin, heat transfers to the environment through radiation, conduction, convection, and evaporation. Arteriovenous shunts directly under the skin can open to allow heat escape or close to retain heat, making blood circulation essential for temperature regulation.
Q6: What role does the sympathetic nervous system play in thermoregulation?
The sympathetic nervous system responds to hypothalamic signals to regulate blood vessel diameter and heat production. When the anterior hypothalamus detects rising temperature, it stimulates the sympathetic nervous system to open arteriovenous shunts and promote vasodilation for heat loss. Conversely, when the posterior hypothalamus detects falling temperature, it signals vasoconstriction to conserve heat.
Q7: Why does the body maintain a constant core temperature despite environmental changes?
The body maintains constant core temperature through complex physiological mechanisms controlled by the hypothalamus, which detects even minor temperature variations. When environmental conditions change or physical exertion increases heat production, the anterior and posterior hypothalamus activate appropriate heat loss or conservation mechanisms, ensuring core temperature stability for optimal cellular function.